Maui County VOC Water Sampling Comparison

Post-fire analysis of volatile organic compound detections across Maui county and lab data

Author

Alemarie Ceria

Published

November 4, 2025

Project Description

This project compiles and standardizes post-fire volatile organic compound (VOC) water sampling data from Maui County to enable comparison with our labโ€™s independent tap water sampling conducted following the August 2023 Lahaina fires. Each dataset contains results for a suite of VOCs (e.g., benzene, toluene, ethylbenzene, xylene) analyzed across multiple sample locations and dates.

Current Task: Get Sampling Coordinates

Task

Webscrape and extract the coordinates of all points within the Department of Water Supply - Water Advisory Area Address Locator Web App.

Tracing Web App Requests to APIs

Locate Feature Service Endpoints

The legend shows that the water samples come from three spatial layers: hydrant, property, and WTP/tank. To see where the data is being pulled from, we need to find the request URLs using the Chrome DevTools (inspect element tool) by:

  1. Going to the โ€œNetworkโ€ tab
  2. Pressing the โ€œFetch/XHRโ€ button to filter to requests
  3. Filtering to PBF data, which holds the feature data by inputting โ€œquery?f=pbfโ€ into the filter bar
  4. Clicking one of the queries within the โ€œNameโ€ box
  5. Inspecting the Request URL to get the base URL

Here, we can see that the water sample data is being pulled from the SAMPLES feature server: https://services3.arcgis.com/fsrDo0QMPlK9CkZD/arcgis/rest/services/SAMPLES/FeatureServer/.

From there, we can see the three layers listed and their IDs. We can also go to the map viewer to confirm if this is actually the data we want to be requesting.

Build Queries

Here are the feature layer base URLs:

  1. Hydrant Water Samples: https://services3.arcgis.com/fsrDo0QMPlK9CkZD/arcgis/rest/services/SAMPLES/FeatureServer/0
  2. Property Water Samples: https://services3.arcgis.com/fsrDo0QMPlK9CkZD/arcgis/rest/services/SAMPLES/FeatureServer/1
  3. WTP/Tank Water Samples: https://services3.arcgis.com/fsrDo0QMPlK9CkZD/arcgis/rest/services/SAMPLES/FeatureServer/2

You can see the parameters you can specify in your query by:

  1. Going to the end of one of the feature layers above
  2. Clicking Query (Example URL: https://services3.arcgis.com/fsrDo0QMPlK9CkZD/ArcGIS/rest/services/SAMPLES/FeatureServer/0/query)

Data Workflow Overview

The figure below shows the automated {targets} pipeline used to download, process, and export water sample data from the Maui County Department of Water Supply ArcGIS feature service.

Summary

  1. Define layers: The feature_layers target lists the three ArcGIS feature server layers (hydrant, property, WTP/tank).
  2. Fetch counts: layer_counts queries how many records each layer contains.
  3. Download: raw_layer downloads each dataset (runs as dynamic branches in parallel).
  4. Tidy: tidied_layer cleans and standardizes each datasetโ€™s columns and location strings.
  5. Merge: merged_ws_sf combines all tidied layers into a single spatial object (sf).
  6. Export: exported_ws_as_x writes the final datasets to/data/03_output/.

Each circle in the graph represents a target (a single object or file), and each square represents dynamic branches that run independently for each layer. See R/ folder in repository for scripts used in pipeline.

Outputs

Interactive Table

Interactive Map

Hover over a point to see location name or click on it to view more details:

Next Task: Parse VOC Results

Task

Clean, standardize, and parse VOC results into long format.

Feedback and Contribution

Have feedback?

Use the simple form (screenshots welcome):

Reproducibility

This project uses renv for dependency management.

Clone the Repository

Pick one method.

HTTPS (easiest)

git clone https://github.com/alemarieceria/voc_ws_comparison.git
cd voc_ws_comparison

SSH (if youโ€™ve set up SSH keys)

git clone git@github.com:alemarieceria/voc_ws_comparison.git
cd voc_ws_comparison

Set Up R Environment

In R/RStudio/Positron/VSCode console:

renv::restore()

Build the Pipeline and Report

In R/RStudio/Positron/VSCode console:

targets::tar_make()

Pipeline Outputs

  1. docs/index.html (Website)
  2. data/02_interim/2025_11_03_raw_ws_locations_sfs_list.RData (Queried data)
  3. data/03_output/2025_11_03_standardized_ws_names_and_locations.csv (Processed dataset)
  4. data/03_output/2025_11_03_standardized_ws_names_and_locations.gpkg (Processed spatial layer)

Session Information and Dependencies

Project directory: F:/shuler_lab_projects/voc_ws_comparison 
R version 4.5.0 (2025-04-11 ucrt)
Platform: x86_64-w64-mingw32/x64
Running under: Windows 11 x64 (build 26200)

Matrix products: default
  LAPACK version 3.12.1

locale:
[1] LC_COLLATE=English_United States.utf8 
[2] LC_CTYPE=English_United States.utf8   
[3] LC_MONETARY=English_United States.utf8
[4] LC_NUMERIC=C                          
[5] LC_TIME=English_United States.utf8    

time zone: Pacific/Honolulu
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices datasets  utils     methods   base     

other attached packages:
 [1] htmltools_0.5.8.1  fs_1.6.6           readr_2.1.5        mapview_2.11.4    
 [5] DT_0.34.0          visNetwork_2.1.4   sf_1.0-21          dplyr_1.1.4       
 [9] tarchetypes_0.13.2 targets_1.11.4    

loaded via a namespace (and not attached):
 [1] bslib_0.9.0             xfun_0.54               raster_3.6-32          
 [4] htmlwidgets_1.6.4       processx_3.8.6          lattice_0.22-6         
 [7] tzdb_0.5.0              callr_3.7.6             leaflet.providers_2.0.0
[10] vctrs_0.6.5             tools_4.5.0             crosstalk_1.2.2        
[13] ps_1.9.1                generics_0.1.4          stats4_4.5.0           
[16] base64url_1.4           parallel_4.5.0          tibble_3.3.0           
[19] proxy_0.4-27            pkgconfig_2.0.3         KernSmooth_2.23-26     
[22] satellite_1.0.6         data.table_1.17.8       secretbase_1.0.5       
[25] RColorBrewer_1.1-3      uuid_1.2-1              leaflet_2.2.3          
[28] lifecycle_1.0.4         compiler_4.5.0          farver_2.1.2           
[31] textshaping_1.0.4       terra_1.8-70            codetools_0.2-20       
[34] sass_0.4.10             class_7.3-23            yaml_2.3.10            
[37] jquerylib_0.1.4         pillar_1.11.1           classInt_0.4-11        
[40] cachem_1.1.0            brew_1.0-10             tidyselect_1.2.1       
[43] digest_0.6.37           rprojroot_2.1.1         fastmap_1.2.0          
[46] grid_4.5.0              here_1.0.2              cli_3.6.5              
[49] magrittr_2.0.4          base64enc_0.1-3         leafem_0.2.5           
[52] e1071_1.7-16            withr_3.0.2             prettyunits_1.2.0      
[55] scales_1.4.0            backports_1.5.0         sp_2.2-0               
[58] rmarkdown_2.30          igraph_2.2.1            hms_1.1.4              
[61] png_0.1-8               evaluate_1.0.5          knitr_1.50             
[64] rlang_1.1.6             leafpop_0.1.0           Rcpp_1.1.0             
[67] glue_1.8.0              DBI_1.2.3               renv_1.1.5             
[70] svglite_2.2.2           rstudioapi_0.17.1       jsonlite_2.0.0         
[73] R6_2.6.1                systemfonts_1.3.1       units_1.0-0

For the complete dependency list, see the renv.lock file.

Environment Status

No issues found -- the project is in a consistent state.